Field of the Invention
The invention relates, in general, to a steam turbine, and in particular, to a steam turbine with a flow duct with blading configured within it and to a blade or vane for a steam turbine.
A turbine blade or vane for use in the wet steam region of the penultimate and final stages of turbines is described in German published, non-prosecuted Patent Application DE 195 46 008 A1. Such a turbine blade or vane is subject to erosive wear due to impinging water droplets. This erosive wear is reduced by the airfoil of the turbine blade or vane having surface roughness in the region of its leading edge and the region of the suction surface of the blade or vane or in at least a partial region thereof, which surface roughness is markedly increased relative to the surface roughness of the pressure surface of the airfoil. A film of water is held on the surface of the turbine blade or vane by this surface roughness. This film of water reduces the erosive effect of impinging water droplets.
German Patent DE 36 095 41 C2 deals with the reduction of the aerodynamic drag of a body in turbulent flow. The reduction in drag is achieved by reducing the turbulent wall shear stress. For this purpose, the surface of the body is provided with ribs in a plurality of rib formations. The ribs are arranged offset to one another laterally to a flow direction and have short extensions in the flow direction. In particular, DE 36 095 41 C2 reveals such a surface structure for reducing the drag of an aircraft wing.
German published, non-prosecuted Patent Application DE 43 19 628 A1 deals with the structuring of turbo-machine surfaces in contact with fluid. The flow losses are minimized by a applying a grooved structure. The special relationships of fluid pumps are taken into account in this publication.
German Utility Model G 90 13 099 relates to a rotor for extracting energy from a flowing medium or for releasing energy to a flowing medium consisting of a hub and at least one rotor blade. An increase in the efficiency of the rotor is achieved by a rotor blade of the rotor having a corrugated shape. In addition to the absolutely necessary corrugated shape, such a rotor blade can also be completely covered with grooving.
An impeller for a centrifugal compressor, in particular for a gas turbine, is described in U.S. Pat. No. 3,481,531. The impeller has vanes which extend radially outward and between which is located an impeller wall. The impeller wall is provided with grooves which extend radially outward so that a boundary layer of gas adhering to the wall is broken up and energy losses are therefore minimized.
U.S. Pat. No. 4,023,350 shows an appliance which reduces a pressure loss in a gas turbine. The appliance consists of a chain of protrusions which extends between two adjacent blades or vanes of a blading ring of the gas turbine. This chain of protrusions acts to generate a vortex so that a boundary layer thickness, and therefore losses due to transverse flows, are reduced.
In the VDI reports No. 1109 of 1994, Jetter and Rie.beta. describe on page 241 of the article "Aerodynamic Properties of Turbine Blading Profiles of Different Manufacturing Qualities", the influence of surface roughness on the efficiency of turbine blading profiles. The article states that surface roughnesses, such as milling grooves, have an influence on the profile loss but, because of the importance of other parameters, this influence cannot yet be accurately quantified.
A steam turbine is considered in the book "Turbo-machines" by Klaus Menny, B. G. Teubner Stuttgart, 1995. It is stated therein that water turbines, steam and gas turbines, windmills, centrifugal pumps and centrifugal compressors and propellers are combined under the collective designation of "turbo-machines". A common feature of all these machines is that they are used for the purpose of withdrawing energy from an active fluid in order to drive another machine or to supply energy to an active fluid in order to increase the pressure of the latter. Using a simple turbine as an example, the mode of operation of a turbo-machine is explained. The active fluid enters the machine and flows first through a blading ring of stationary guide vanes. This increases the velocity and therefore the kinetic energy of the active fluid. Its pressure and therefore its potential energy are reduced. At the same time, the shape of the guide vanes produces a velocity component in the peripheral direction of a rotor blade ring downstream of the guide vane ring. By means of the rotor blade ring, the active fluid gives up its kinetic energy to the rotor, to which the rotor blade ring is connected, because the direction and frequently also the magnitude of the velocity of the active fluid is changed when flowing over the rotor blades. The rotor blade ring is made to rotate. The active fluid emerges from the machine with reduced energy content. The ratio between the mechanical energy gained from the turbine and the energy withdrawn from the active fluid characterizes the efficiency of the turbine.